Demon invasion.

I built 10% of the summoning structures quite quickly. But there's a problem with combat buildings: if there's an ore mine, there's no wood. Wolves can't be defeated right away. You build Imps and unupgraded Demons, and that's where it ends. With these Imps, unupgraded Demons, and random troops from the refugee camp, you can't kill much. My hero has problems precisely because of the lack of combat buildings and the inability to build them, while the average neutral army consists of 4th-level creatures. You spend a week gathering troops, always upgrading them, sacrificing 1 Imp at the altar for 2 luck points, and all of this allows you to fight 1-2 battles a week with a good percentage of losses (the losses themselves are small, but the percentage of losses is high, even for the same ore mine). If you're lucky with the ballista, it's okay, but if not...

Near the second castle, everything shoots, especially the Elves along the way to it; you can't get there without being well-developed.

That portal was guarded by 500+ Manticores. I wouldn't have been able to pass them even if the author hadn't made them 7th-level undead with a small set of spells, but even if they were the same useless creatures as before, they still couldn't be defeated :) you could only hide in your Necropolis.

I passed the Knights of Death because of the narrow passage using the Crystal of Secret Knowledge